1. Field of Invention
The present invention relates to the field of an integrated circuit, and more particularly to a circuit for outputting reference voltage.
2. Description of Related Arts
The circuit for outputting reference voltage is mainly used for providing a stable voltage outputted, and the voltage outputted thereof serves as a reference for other circuits. The circuit for outputting reference voltage has characteristics of having temperature compensation, little affection by power source and temperature, high precision and etc., and thus is widely applied in structures of various circuits.
As is well known, the circuit for outputting reference voltage comprises a plurality of field effect transistors (FETs). However, the output voltage of the circuit for outputting reference voltage usually is not varying with foundry corner of the FETs; while in some special circuits such as oscillator, because the foundry corner of the FETs has a great effect on the frequency of the oscillator, it is usually necessary for compensating the foundry corner, so as to output a constant frequency thereby. In this situation, the conventional circuits for outputting reference voltage are not capable of meeting the requirements. Therefore, it is necessary to provide a circuit for outputting reference voltage having output voltage capable of varying with the foundry corner of the FETs. Furthermore, in order to avoid the output voltage from being affected by temperature, the circuit should have temperature compensation as well. In addition, the foundry corner of the FETs refers to parameter variation of the FETs in the manufacture process of the FETs due to position differences on one wafer, or between wafers of different batches.